雙離子添加之氧化鉍((Bi0.887Sr0.06Nb0.053)2O3.046)離子導體與鈣鈦礦型導電氧化物相穩定性之研究

Abstract

When Solid oxide fuel cell working durance 600℃-800℃, interface resistance raise between electrolyte and electrode result as decreasing efficiency of SOFC. High ionic conductivity electrode or composite electrode consisting of electrolyte and electrode replace traditional electrode (poor ionic electrode)result as raise reaction area of oxygen and reducing interface resistance. In this research, using composite electrode consisting of perovskite type conducting oxide (La0.75Sr0.25CuO2.5 (LSCu), La0.8Sr0.2MnO3 (LSM) and Y0.5Sr0.5MnO3 (YSM)) and Bi2O3 based electrolyte as cathode of SOFC. The composite electrode decreased interfacial resistance and raise efficiency of SOFC. By doping Nb2O5 into (Bi2O3)0.73(SrO)0.27 rhombohedral structures, the rhombohedral structures were able to stabilize to cubic structures which have high conductive property. ((Bi2O3)0.73(SrO)0.27)0.85(Nb2O5)0.15 were δ phase and SrBi2Nb2O9 coexisted. The composition of the δ phase was analyzed by SEM/EDS analysis, and found to be (Bi0.887Sr0.06Nb0.053)2O3.046 (SNB). The single δ phase (Bi0.887Sr0.06Nb0.053)2O3.046 shows higher conductivity of 2.42*10-2S/cm at 450˚C. In the perovskite-SNB mixed powder, the reactivity in the high temperature is: LSCu-SNB >LSM-SNB>YSM-SNB. LSCu reacted with SNB as La0.3Bi0.7O1.5 and Bi2Sr2CuO6 when annealing temperature upon 700℃. LSCu phase decomposed to La2CuO4 and CuO phase. In LSM-SNB system, LSM reacted with SNB to form rhombohedral phase. In YSM-SNB system, no extra phases appear in the XRD pattern after annealing at 800℃ for 20h. However, the peak intensity of YSM reduced due to diffusion of atoms. In order to check diffused atom, analysis by diffusion couple. La-Bi oxide and Bi-Cu oxide reaction layer are observed in the LSCu-SNB. According to XRD pattern of LSCu-SNB mixed powder, Bi-Cu oxide reacted with Sr ions as Bi2Sr2CuO6 after annealing for a long time. In the LSM-SNB system, reaction zone was presented by non-layer in the LSM side. The dotted Bi rich zone spread in the LSM matrix. The Bi rich zone is rhombohedral phase La3+ doped bismuth oxide. In YSM-SNB system, Sr2+ reacted with Bi3+ as Sr-Bi oxide. Three systems were observed secondary phase (SrBi2Nb2O9) in the SNB side due to diffusion of Bi3+. The over-potential of semi-cell (perovskite-SNB/SNB/Pt) was measured by current-interruption technique. YSM-SNB composite electrode and SNB electrolyte has the lowest over-potential among three systems. YSM-SNB composite electrode was more suitable for SNB electrolyte than LSCu-SNB and LSM-SNB.